Method of making porous metal



Feb. 15, 1944. R. G. OLT

,METHOD OF MAKING POROUS METAL Filed Aug. 2s, 1941 INVENTOR A RICHARD 6.01.1'4

a-Y 44u Manu 9 i ATTORNEYS Patented Feb. 15kl944;

e mmv METHOD OF MAKING POROUS METAL Richard G. Olt, Dayton, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corpora-` tion of Delaware Application August 28, 1941, Serial No. 408,667

claims;

This invention relates to a method and apparatus for forming porous metal articles and is particularly concerned with methods and apparatus for centrifugally forming porous metal articles.

An object of the invention is to provide a method for forming cylindrical objects from powdered metal wherein the powdered metal is distributed into cylindrical form and, while being held in place centrifugally. is sintered for forming a porous metal cylinder.

A further object of the invention is to provide an apparatus for carrying out the above object.

Another object-of the invention is to provide a method of centrifugally forming objects from powdered metal wherein sintering of the powdered metal is accomplished by the use of inductive heating.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

-In the drawing:

Fig. l is a view in cross section showing the apparatus as the powdered metal is being filled therein.

Fig. 2 -is a view in cross section showing the powdered metal being leveled oif into a cylindrical form.

Fig. 3 is a view in cross section showing the heating element in place during the sintering of the powder.

Fig. 4 is aview of the cup which flts in the rotatable receptacle. r v

Fig. 5 is a view of the complementary cup which ts in the cup shown in Fig. 4.

Fig. 6 is a perspective view of the rotatable receptacle.

` cylindrical objects it is-necessary to put draft on the core portions of the mold and on the wall portionof the mold so that the article may be removed therefrom after sintering, otherwise it is necessary to destroy the mold in order to remove the article therefrom.

The present invention is directed to a method and apparatus wherein cylindrical objects may be formed without the use of cores and wherein the apparatus utilized may be reused any number of .times to form cylindrical articles of like shape and dimensions. The invention takes advantage of centrifugal force as a means for distributing the metal powder for holding it in place during sintering. To this end a rotating` cylinder having a refractory lining is provided into whichv a charge of metal powder is placed. The charge may be inserted into thecylinder during rotation thereof or while the cylinder is stationary after which the receptacle is rotated to a speed sufllcient to cause the metal powder to remain in place adjacent the wall of the cylinder. Next, the scraper is inserted and the metal powder is leveled off into a substantially uniform cylindrical layer. After the cylindrical layer has been formed the metal powder is heated under suitable conditions to sinter the same whereupon the porous metal article may be removed from the apparatus. In this manner no cores are required and no draft is required on any apparatus since, as will be described hereinafter, suitable mold cups are utilized which may be split' to remove the cylindrical objects therefrom.

Referring to the drawing and particularly to Fig. 1, an apparatus 20 is shown which may be used in centrifugally forming cylindrical porous metal articles. Apparatus 20 comprises an outside receptacle 22 which has a shaft 24 extending therefrom. The shaft 24 is preferably journalled in a suitable bearing 26 and the shaft may be connected to motivating means, not shown, whereby the receptacle 22 may be rotated at any desired rate oi speed. 'I'he walls 28 of cavity within receptacle 22 are tapered outwardly so that the diameter at the outer end of the receptacle is greater than the inner end thereof. Within this cavity is tted a complementary tapered cup 30 which is preferably made in two pieces and which snugly fits against the walls 28 since the cups outer walls are of a truncated conical shape complementing the shape of the cavity walls. The inner surface 32 of cup 30 is also of a truncated conical shape and is adapted to receive a split cup 34 made in two portions which are split longitudinally of the cup. The

cup 34 has a cylindrical inner surface and a truncated conical outward surface 36 which is complementary to the inner 32 of cup 30, whereby the two portions of cup 34 may be assembled and slipped within the cup 30 and then the cup 30 may be -slipped within the receptacle 22. The cup 30 and cup 34 include end flanges 38 and 40 respectively thereon which flanges preferably have the same inner diameter. Thus when the assembly is placed within the receptacle 22 as shown in Fig. 1, a cylindrical surface is presented which is adapted to receive metal powder 42 which is fed from a suitable dispenser 44. The powder is preferably fed into the apparatus while the, receptacle 22 is rotated at a high rate of speed. After the dispenser 44 is removed from the apparatus, a scraper 46 is inserted therein and while resting `on flanges 38 and 40 scrapes the powder into a substantially uniform cylindrical layer. If a measured quantity of powder has not been supplied to the apparatus excess powder may be scraped outwardly of the cup 34 by proper positioning of the apparatus. In any event, after the scraper 46 has completed its operation, a cylindrical layer of metal powder is apparent within the apparatus which is rotatingat suiiciently high speeds to maintain the powder in place.

The receptacle portion of the apparatus is heated by suitable means, electrically or otherwise, to a temperature and ior a time suflicient to cause the metal powder to sinter together into a porous metal layer. I prefer to use an inductive heating means B8 as shown in Fig. 3 which comprises a cup 50 having an induction heating coil 52 disposed around the inner surface thereof which coil and cup are adapted to iit over the outside of the rotating receptacle 22. At the axis of the cup 48, a tube 54' is'provided through which a controlled atmosphere may be admitted to the cavity in which the powdered metal is being sintered. By using inductive heating, it is possible toget very rapid action in sintering, thereby reducing the time required for the operation. fAfter the current is turned off, the controlled atmosphere can be admitted to the cavity for cooling purposes, after which the heating element 48 is removed and the cups 30 and 34 are taken out of the receptacle and disassembled for removing the cylindrical article therefrom. The cups and receptacle may be made from any suitable material such as heat resisting steels wherein the contacting surfaces are treated for preventing` adhesion at the elevated temperatures. 4Similarly the cups may be made from refractory material such as graphite, ceramics or the like. If the inner cup 34 is removed and the inner vWall 32 of cup 31E is made straight sided and provided. with a bottom it ispossible to make articles therein'in cupped shapes which have a bottom wall with cylindrical or substantially cylindrical side walls. In this instance, it is preferred to have the cup Sii split -so that the article can be removed therefrom without the necessity of draft. When desired, the inductive heating element may be inserted' within the cup cavity so as to surround the tube 54. In this case, the tube must be made of a non-inductive material while the outer cups and receptacle cylinder or cups, conical cups or any other shape possible to be made centrifugally.

While the embodiment of the present invention as herein disclosed. constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In the method of making hollow cylindrical porous metal articles the steps comprising, supplying a measured quantity of powdered metal to a receptacle rotating axially thereof at a speed suicient to cause the powdered metal to remain in contact with the walls thereof, scraping the powdered metal into a uniform layer within the receptacle for forming a cylindrical body, then heating the receptacle with the powdered metal therein, while the receptacle is rotatlng at said rate of speed and lunder suitable conditions of time, temperature .and atmosphere for causing the'powdered metal to sinter together into a highly porous metal layer, and then cooling the cylindrical article so formed and removing it from 'the receptacle.

2. In the method of making hollow cylindrical bodies of porous metal in the loose noncompacted condition, the steps of supplying metal powder to a receptacle, rotating the receptacle axially thereof at a speed sufiicient to' ,centriiugally distribute the powder adjacent the walls of the receptacle, leveling the powderedv metal .in the receptacle into a uniform thickness layer, and then,'while thev receptacle is rotatingfheating the-receptacle with the metal powder therein under suitable conditions of time, temperature and atmosphere for causing the metal powder to sinter together and form a highly porous cylindrical object which may be removed' from the receptacle after cooling.\

3. In the method of making hollow cylindrical objects of highly porous metal the steps comprising: centrifugaily distributing e. charge of metal powder into a. substantially uniform layer 'of cylindrical shape by axially rotating a mold member, and then heating said layer while ythe layer is being held in place in said member by centrifugal force, said heating being accomplished under suitable conditions of time, temperature and atmosphere to form a highly porous cylindrical body.

4. The method as claimed in claim 3 wherein the heating is accomplished by the-use of an inductance coil.

5. In the method of making -hollow cylindrical porous metal bodies, the steps of: providing a cylindrical receptacle capable of being rotated, supplying metal powder to said receptacle while the receptacle is being rotated axially thereof at a speed suiiicient to hold the metal powder adjacent the wall thereof, leveling the metal powder into a substantially uniform cylindrical layer, inductively heating the metal powder for a time and at a temperature sumcient to bond the particles together for forming-a porous metal body, and simultaneously providing an atmosphere suitable for sintering adjacent said metal A powder layer.

RICHARD G. OLT. 

